This invention relates to a reference voltage generator which provides a predetermined DC voltage correctly and stably from a constant DC voltage.
For example, a converter for converting a digital signal to an analog signal, a converter for converting an analog signal to a digital signal and other various types of converters require a reference voltage, and the accuracy of such equipment may sometimes depend on the accuracy of the reference voltage; therefore, it is important to obtain a highly accurate, stable reference voltage.
In a conventional reference voltage generator, a constant voltage is obtained by a Zener diode and amplified by a variable gain DC amplifier, and its gain is adjusted to obtain a reference voltage of a predetermined magnitude. Accordingly, it is necessary to set up the gain of the DC amplifier with high accuracy, and the setting of the gain is effected by controlling the resistance value of a resistor used in the amplifier. In order to obtain a resistor having a correct resistance value, it is necessary to regulate the resistance value, and since the resistance value is affected by temperature variations, if a winding resistor of high stability is employed, the circuit arrangement becomes bulky and expensive. In the case of using a thin film resistance element, the adjustment of its resistance value requires special equipment and much trouble, and on top of that, the resistance value is subject to the influence of a temperature change. Thus, the DC amplifier is pre-adjusted and is difficult to re-adjust. Consequently, since there is dispersion in the constant voltage value available from the Zener diode, if the Zener diode breaks down, it is necessary to replace the reference voltage generator in its entirety with a new one.